Our determinations of structure of bacterial iron-containing proteins, some functional in bioconversion of solar energy, are being extended by a survey of marine microorganisms. New specimens of protein previously seen in terrestrial species, are being found and enable conclusions to be drawn on adaptation to high-salt environment. These include variant cytochromes c (c2, c'), a number of high potential iron-sulfur proteins ("HiPIP"), and several examples of hydrogenase. A rationale for stabilization of air-labile hydrogenase dependent on non-covalent adsorption to polycationic media has been demonstrated to lead in a simple fashion to stabilization factors greater than 3000-4000 fold.